The present invention relates to a process and apparatus for making sealed filter units. In particular the present invention relates to an apparatus and process for sealing a plurality of filter elements to a filter element assembly so that the integral filter element assembly may be combined with a housing member to form a sealed filter unit.
Molded plastic filters and filter units are well known and enjoy a wide use and general acceptance in a variety of industries. The function of such units is to remove contaminants from liquid or gaseous materials which flow therethrough. These units are particularly important in the medical industry wherein they are used to filter bacteria, gasses and other contaminants from solutions before being introduced into the human blood stream. In such critical applications it is imperative that the filtrate not bypass the filtering elements. It is necessary, therefore, to provide a leakproof filter unit so as to prevent leakage around the filter element and to prevent possible bacteria contamination from outside the assembly.
Typically, the filter units used to filter intravenous solutions comprise a two-part housing with an internally disposed filter sandwiched therebetween. Typically, the molding process for these filter units entails, first the molding of the filter element support member, which is usually the outlet housing member of the filter unit. Once the filter element support member has been molded, through injection molding, a filter element is usually located on the outlet housing member over the outlet opening. Once so located, either an overmold is molded over the outer peripheral edge of the filter element and the outlet housing member, encapsulating the filter element within the outlet housing member, or the inlet housing element is positioned over the outlet housing member sandwiching the filter element therebetween. The inlet housing member and outlet housing member are then sealed together by any of a variety of methods including, pressure clamping, heat sealing, ultrasonic welding, or the use of an overmold band. See, e.g., U.S. Pat. No. 4,113,627.
It is especially critical in the medical industry to maintain a leakproof seal between the filter element and the filter housing members. Thus, it is essential that the filter elements are properly positioned on the housing member to insure that the fluid which is being filtered does not bypass the filter elements. When only one filter element is to be positioned on the housing member, this operation can usually be accomplished without much problem.
When a plurality of filter elements are to be positioned on a housing member, not only is the problem of properly locating the filter elements on the housing member compounded, but also a second problem of aligning the filter elements with each other is created. With regard to this problem, it should be noted that the majority of filter elements used in the medical industry are not flat pieces of membrane, but usually have a textured, uneven surface. Thus, for example, when seven to nine filter membranes are stacked, they have a height of approximately one-eighth to one-sixth of an inch.
Furthermore, not only is there a problem of positioning and aligning a plurality of filter elements on the housing member, once they are so aligned their lateral movement with respect to the filter element support and each other must be prevented so that they may be secured to the housing member.
Thus, there is a need for a new process and apparatus which will properly locate and align a plurality of filter elements on a filter element support and maintain that location while the filter elements are sealed into an integral filter element assembly.